The invention relates to radiation detectors generally, and relates more particularly, but not exclusively, to such detectors as are used for detecting low energy radiation. BACKGROUND OF THE INVENTION
The term xe2x80x9cradiationxe2x80x9d as used herein refers to any type of ionizing radiation of various energies. By xe2x80x9clowxe2x80x9d energy radiation is meant radiation having energies below 3xc3x97105 eV (electron Volts).
Radiation detectors are used in medicine, industry, and research to obtain structural information. Materials transmit and absorb radiation energies in different ways. These differences may be used to gain valuable insight into the nature of the material through which the radiation has passed. A radiation detector typically converts the radiation to visible light, which may then be converted further to an electrical signal and appropriately processed to yield the desired information.
One common type of radiation detector is a geophysical wireline logging type which is lowered into the bore of a well to gain information about the well condition and the properties of the surrounding geological formations. An example of such a detector is described in U.S. Pat. No. 5,070,249 entitled xe2x80x9cPhotomultiplier Tube Mounting for Well Logging Detectorsxe2x80x9d issued Dec. 3, 1991 to J. A. White and U.S. Pat. No. 5,744,803 entitled xe2x80x9cRadiation Detector Assembly and Method with Discrimination Between Vibration and Radiation Induced Eventsxe2x80x9d issued Apr. 28, 1998 to C. M. Grodsinsky, both assigned to the present successor assignee. Such detectors have a cylindrical metal housing in which there is disposed a scintillation crystal coupled to a photomultiplier tube (PMT). Radiation passes through the wall of the housing into the crystal. There it is converted to visible light which passes to the PMT for conversion into an amplified electrical signal. The signal is led out of the housing and up a wire to a receiving station for processing and interpretation.
Another type of detector is placed at the outside surface of a well output pipe in order to gain spectral information about the fluids flowing in it by sensing low energy radiation which has passed from a source through the fluids. The information can be used to determine fluid constituent proportions and flow parameters.
The housing of a geophysical logging detector is generally a rugged metal cylinder, typically of stainless steel or aluminum, which is hermetically sealed at both ends by end caps in order to protect the internal components from contamination and mechanical damage. These metals and some others are relatively transparent to most of the radiation of interest. However, they are not very transparent to low energy radiationxe2x80x94gamma and x-rays. In order for it to pass a sufficient fraction of such low energy radiation, it would be necessary to make the metal of the housing so thin that it would become very subject to mechanical deformation in use and also unreliable in preventing contamination of its internal components by fluid intrusion.
There is therefore a need for a detector with a housing which is hermetically reliable and highly transparent to low energy radiation while also being at the same time opaque to light and sufficiently mechanically rugged to be able to withstand the down-hole wireline environment.
In accordance with the present invention a radiation detector is provided with a housing having a laminated carbon fiber composite wall which is opaque, hermetically reliable, mechanically rugged, and highly transparent to even low energy ionizing radiation.